Q: If I backup my photos to icloud and delete those photos from my ipad can I download the photos back to my ipad?

Are you using iCloud Photo Library or backing up your camera roll?

If iCloud Photo Library then I think the answer is no. I believe when you delete them from one place you delete them from everywhere. If you want to do that I'd use Dropbox or something or store them on a computer.

Here are some Apple Support documents on the subject ...

Choosing an iOS Backup Method (Should I Use iTunes or iCloud to back up ...)

https://support.apple.com/kb/HT5262

Back up and Restore your iOS Device with iCloud or iTunes

http://support.apple.com/kb/ht1766

iTunes: About iOS Backups

http://support.apple.com/kb/ht4946

Create and Delete iPhone, iPad and iPod Touch Backups in iTunes

http://support.apple.com/kb/ht4946

iOS: Troubleshooting Encrypted Backups

http://support.apple.com/kb/TS5162

Get Help in finding Your Photos in iOS 8 or later

http://support.apple.com/kb/HT6464

iCloud Photo Library Beta FAQ

http://support.apple.com/kb/HT6378

iCloud: Set up my Photo Stream

http://support.apple.com/kb/PH13693

No, that's not the right answer ... if you are using "iCloud Photo Library", then you can erase ypur photos from your iPad and they will stay in "iCloud Photo Library". That is the intended functionality of that service.

HOWEVER, having said that, one must realize that right now "iClould Photo Library" is still in BETA and that you are a Beta Tester right at the moment, and that it's not guaranteed that a Beta Service will be acting the way it's supposed to ... until it gets to the final release.

I thought I would add something here. If you want to use another backup service for right now, you could try Dropbox. It will save all your photos "in the cloud" (on their service). It's real easy to use, as they have an app that goes with the service, and the upload to the cloud is pretty automatic. I'm using Dropbox for about 5,000 photos right now, and doing my iCloud Backup on top of that. And hopefully, when "iCloud Photo Library" is "final" ... I'll be using that.

Well, I am revisiting this question, because I came across an Apple Support FAQ on the subject, and it said that deleting a photo from the iPad would delete the photo from iCloud Photo Library. But, then again, another user posted that he knew a way around that happening.

SO ... for right now just remember that "iCloud Photo Library" is in beta and if you use it, that means you have agreed to be a "beta tester" for this service and you'll report to Apple any problems or bugs. And also remember that being in "beta" means that you can lose your photos at any time (that are in iCloud Photo Library") and there is no way Apple will get them back to you. You have been warned now!

ALSO ... be aware that if you use "iCloud Photo Library" that you will have NO BACKUP in the "iCloud Backup" that you may have been using in the past (as I have been using in the past and was depending on it to insure my photos would be safe). When using "iCloud Photo Library" it turns OFF your "iCloud Backup" for your photos!

Here's the Apple Support document ...

iCloud Photo Library Beta FAQ

http://support.apple.com/kb/HT6378